Strain insulator for dead ending



Dec. 13, 966 J. o. SWEENY ETAL 3,291,900

STRAIN INSULATOR FOR DEAD ENDING 2 Sheets-Sheet 1 Filed Aug. 9, 1965 Dec. 13, 1966 J. o. SWEENY ETAL 3,291,900

STRAIN INSULATOR FOR DEAD ENDING 2 Sheets-Sheet 8 Filed Aug. 9, 1965 United States Patent flfice 3,291,900 STRAIN INSULATOR FQR DEAD ENDENG James 0. Sweeny, Pittsfield, Mass, and William D. Becker, Baltimore, Md, assignors to General Electric Company, a corporation of New York Filed Aug. 9, 1965, Ser. No, 478,164 8 Claims. (Cl. 174169) This invention relates to strain insulators and more particularly to strain insulators for dead ending.

The conductors of overhead open wire electric power and distribution lines are conventionally supported and insulated from tower or pole crossarms by either pin type insulators or post type insulators or suspension type strain insulators. However, such insulators are not suitable for directly supporting the conductors at the ends of the line. Heretofore, this dead ending, as it is called, has usually been done by assembling an extension link, a multiplicity of suspension type strain insulators, and a cable clamp into a string.

In accordance with this invention, there is provided a new and improved unitary inorganic fiber core molded plastic sheathed strain insulator for dead ending.

An object of the invention is to provide a reduced size, light weight, less costly insulator for dead ending that is easier to install and easier to insulate for hot line maintenance than conventional insulator strings for dead ending.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing,

FIG. 1 is a perspective view of a conventional prior art dead ending string,

FIG. 2 is a similar view of the present invention,

FIG. 3 is a section on line 33 of FIG. 2 at the clamp end, and

FIGS. 4 and 5 are sectional views at right angles to each other of the bail or clevis end, FIG. 5 being a section on line 5-5 of FIG. 4.

Referring now to the drawing, and more particularly to FIG. 1, a conventional dead ending string comprises a plurality of suspension type strain insulators I linked together and attached at one end to a cable clamp 2 and at the other end to a steel extension link 3 having a clevis 4 at the outer end thereof.

Referring now to FIG. 2, the insulator of the present invention is a unitary construction, the central portion of which is a molded plastic sheath 5 on which may be formed a plurality of axially spaced circular skirts 6 with one end permanently anchored to a cable clamp 7 and the other end having formed therein an integral bail or clevis 8. Preferably the sheath is made of epoxy resin having a filler of 40 to 80 percent by weight hydrated alumina for preventing creep tracking under the combined effect of electrical stress and surface contamination.

As shown more clearly in FIGS. 3, 4, and 5, the central insulating portion has an elongated core 9 of inorganic fibrous material, preferably stranded fiber glass. As shown in FIG. 3, the clamp end is conically flared at 10 and is positioned in an inwardly flaring or flared socket or cavity 11 in the clamp 7. The outer or small end of the socket is enough larger than the outer or large end of the flared end of the core to receive the latter. The

329L900 Patented Dec. 13, 1966 material of the sheath 5 extends into the cavity 11 and fills the space therein not occupied by the flared end 10 of the core 9 so that when the material of the sheath 5 is cured and hardened the strain carrying insulating parts are firmly anchored in the clamp 7.

As shown in FIG. 4, the core 9 at the bail end is formed into a loop 12 which is linked with a metallic wire or cable bail 8 so as to form a clevis. Preferably, a stress distributing thimble of any suitable material such as metal is inserted between the interlinking portions of the bail 8 and the loop 12. The parts 12 and 13 are entirely embedded in the end of the sheath 5 so that only the clevis end of the bail extends therefrom.

For holding the core in compacted form near its ends prior to sheathing, it may be provided with a suitable wrapping as shown at 14.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What We claim as new and desire to secure by Letters Patent of the United States is:

1. A unitary molded strain insulator for dead ending comprising, in combination, an elongated core of stranded inorganic fiber, a bail linked with one end of said core, a cable clamp having a socket receiving the other end of said core, and a molded plastic sheath covering said core, extending into said socket and enclosing the portion of said bail linked with said core.

2. An insulator as in claim 1 in which said socket and other end of the core have generally conical surfaces whose largest diameters are axially outwardly of their smallest diameter.

3. An insulator as in claim 2 in which the smallest diameter of said socket is greater than the largest diam eter of said other end of the core.

4. An insulator as in claim 1 in which said socket is any curved surface and the end of the core received by said socket has a generally parallel curved surface contiguous thereto.

5. A unitary molded strain insulator for dead ending comprising, in combination, an elongated core of fiber glass strands having a loop at one end with the other end conically flared, a metallic bail linking said loop, a cable clamp having an inwardly flared cavity surrounding the conically flared end of said core, and a molded epoxy resin sheath for said core, said sheath enclosing said loop with said bail extending therefrom and filling the space in said cavity not occupied by the flared end of said core.

6. An insulator as in claim 5 with a plurality of integral axially spaced circular skirts on said sheath.

7. An insulator as in claim 5 with a metallic thimble between said bail and said loop embedded in said sheath.

8. An insulator as in claim 5 in which the epoxy resin sheath has a filler of 40 to percent by weight hydrated alumina to prevent creep tracking under the combination of electrical stress and surface contamination.

LARAMIE E. ASKIN, Primary Examiner. 

1. A UNITARY MOLDED STRAIN INSULATOR FOR DEAD ENDING COMPRISING, IN COMBINATION, AN ELONGATED CORE OF STRANDED INORGANIC FIBER, A BAIL LINKED WITH ONE END OF SAID CORE, A CABLE CLAMP HAVING A SOCKET RECEIVING THE OTHER END OF SAID CORE, AND A MOLDED PLASTIC SHEATH COVERING SAID CORE, EXTENDING INTO SAID SOCKET AND ENCLOSING THE PORTION OF SAID BAIL LINKED WITH SAID CORE. 